A suitcase slides 5m along a platform under the action of three different single forces.
(i) A 20N braking force acting opposite to the motion.
(ii) A 50N vertical force acting at right angles to the motion.
(iii) A 10N force of friction acting opposite to the motion for the entire slide.
Which force does the greatest amount of negative work? Write only (i), (ii) or (iii).